Curious?

Something odd here. The BBC website reports:

"Eight people are being held following an anti-terrorist police operation across England to target people they suspect of plotting attacks abroad.
The raids, which began at 0300 BST and involved 500 officers, are believed to relate to activities in Iraq.
Nineteen properties were raided and 10 arrests were made, but two people were later released.
The police forces involved are Greater Manchester, West Midlands, Cleveland, Metropolitan Police and Merseyside."

None of the media seems to be asking questions, so here goes. 500 officers, all on overtime, for 10 arrests? 50 officers per arrest? Did something go wrong? How many did they hope to arrest? As it is an anti-terrorist operation, I suppose we will never have answers to these questions.